Which undefined terms are needed to define parallel lines?
The undefined terms needed to define parallel lines are ‘lines’ and ‘points.‘
Undefined Terms in Geometry
Words used in geometry can be categorized as defined terms and undefined terms. An undefined term is a geometrical word that we cannot describe using other geometrical terms, whereas a defined term is a geometrical word or phrase that we can describe using other geometrical terms. We can use undefined terms to define defined terms.